As portable mobile devices proliferate, there is a growing demand to continuously and accurately know the geographic location of the mobile devices. There are basically two different ways to determine the geographic locations of a mobile device, either using a wireless positioning network such the GPS system or using a database of wireless beacons and determining position using this database.
The first technique suffers from the difficulty in continuously obtaining signals, e.g., from a network of satellite, to enable the position of the mobile device to be determined. It is recognized that such difficulties commonly arise in enclosed areas and confined areas, such as in areas with a large concentration of tall buildings and in tunnels.
The second technique requires the creation of a database of wireless beacons, and the mobile device to be within range of a plurality of such wireless beacons. In the absence of wireless beacons within range, the position of the mobile device cannot be determined.
For the second technique, several systems are being used to enable mobile devices to determine their position. One such system is Place Lab. Place Lab is software providing low-cost, easy-to-use device positioning for location-enhanced computing applications. The Place Lab approach is to allow mobile devices such as notebook computers, PDAs and cell phones, to locate themselves by listening for radio beacons such as 802.11 access points, GSM cell phone towers, and fixed Bluetooth devices that exist in the surrounding environment. These beacons all have essentially unique identifications, for example, a MAC address. The devices compute their own location by hearing one or more IDs, looking up the associated beacons' positions in a stored map, and estimating their own position referenced to the beacons' positions. Additional information about Place Lab is found in: Place Lab: Device Positioning Using Radio Beacons in the Wild, by Anthony LaMarca et al., Pervasive 2005, Munich, Germany; Challenge: Ubiquitous Location-Aware Computing and the “Place Lab” Initiative, by Bill N. Schilit et al., Proceedings of The First ACM International Workshop on Wireless Mobile Applications and Services on WLAN (WMASH 2003), San Diego, Calif. September 2003; A Case Study in Building Layered DHT Applications, by Yatin Chawathe et al., January 2005; Accuracy Characterization for Metropolitan-scale Wi-Fi Localization, by Yu-Chung Cheng et al., Proceedings of Mobisys 2005, January 2005; Social Disclosure of Place: From Location Technology to Communication Practices, by Ian Smith et al., Pervasive 2005, Munich, Germany; and Privacy and Security in the Location-enhanced World Wide Web, by Jason I. Hong et al., Proceedings of Ubicomp 2003, Seattle, Wash. October 2003.
Another positioning system is that of Skyhook Wireless which uses a database of known Wi-Fi access points to calculate the precise location of any Wi-Fi enabled device. For this system, known Wi-Fi networks are mapped, e.g., by having hired drivers travel every street in a neighborhood, and a user's location is calculated based on the Wi-Fi networks the Wi-Fi enabled device detects at a given moment using proprietary software. If the device can identify three networks, it can determine its position, e.g., using triangulation. The more networks the device detects simultaneously, the more accurate the locational fix.